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Register a new userSpin-flop transition in antiferromagnetic multilayers
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A comprehensive theoretical investigation on the field-driven reorientation transitions in uniaxial multilayers with antiferromagnetic coupling is presented. It is based on a complete survey of the one-dimensional solutions for the basic phenomenological (micromagnetic) model that describes the magnetic properties of finite stacks made from ferromagnetic layers coupled antiferromagnetically through spacer layers. The general structure of the phase diagrams is analysed. At a high ratio of uniaxial anisotropy to antiferromagnetic interlayer exchange, only a succession of collinear magnetic states is possible. With increasing field first-order (metamagnetic) transitions occur from the antiferromagnetic ground-state to a set of degenerate ferrimagnetic states and to the saturated ferromagnetic state. At low anisotropies, a first-order transition from the antiferromagnetic ground-state to an inhomogeneous spin-flop state occurs. Between these two regions, transitional magnetic phases occupy the range of intermediate anisotropies. Detailed and quantitative phase diagrams are given for the basic model of antiferromagnetic multilayer systems with N = 2 to 16 layers. The connection of the phase diagrams with the spin-reorientation transitions in bulk antiferromagnets is discussed. The limits of low anisotropy and large numbers of layers are analysed by two different representations of the magnetic energy, namely, in terms of finite chains of staggered vectors and in a general continuum form. It is shown that the phenomena widely described as ``surface spin-flop are driven only by the cut exchange interactions and the non-compensated magnetic moment at the surface layers of a stacked antiferromagnetic system.
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Equilibrium spin configurations and their stability limits have been calculated for models of magnetic superlattices with a finite number of thin ferromagnetic layers coupled antiferromagnetically through (non-magnetic) spacers as Fe/Cr and Co/Ru multilayers. Depending on values of applied magnetic field and unaxial anisotropy, the system assumes collinear(antiferromagnetic, ferromagnetic, various ferrimagnetic) phases, or spatially inhomogeneous (symmetric spin-flop phase and asymmetric, canted and twisted, phases)via series of field induced continuous and discontinuous transitions. Contrary to semi-infinite systems a surface phase transition, so-called surface spin-flop, does not occur in the models with a finite number of layers. It is shown that discrete jumps observed in some Fe/Cr superlattices and interpreted as surface spin-flop transition are first-order volume transitions between different canted phases. Depending on the system several of these collinear and canted phases can exist as metastable states in broad ranges of the magnetic fields, which may cause severe hysteresis effects. The results explain magnetization processes in recent experiments on antiferromagnetic Fe/Cr superlattices.
Magnetocrystalline anisotropy is essential in the physics of antiferromagnets and commonly treated as a constant, not depending on an external magnetic field. However, we demonstrate that in CoO the anisotropy should necessarily depend on the magnetic field, which is shown by the spin Hall magnetoresistance of the CoO | Pt device. Below the Neel temperature CoO reveals a spin-flop transition at 240 K at 7.0 T, above which a hysteresis in the angular dependence of magnetoresistance unexpectedly persists up to 30 T. It is most likely due to the presence of the unquenched orbital momentum, which can play an important role in antiferromagnetic spintronics.
Recent developments in two-dimensional (2D) magnetism have motivated the search for novel van-der Waals (vdWs) magnetic materials to explore new magnetic phenomenon in the 2D limit. Metal thiophosphates, MPX3, is a class of magnetic vdWs materials with antiferromagnetic (AFM) ordering persisting down to the atomically thin limit. The magnetism in this material family has been found to be highly dependent on the choice of transition metal M. In this work, we have synthesized the intermediate compounds Ni1-xMnxPS3 (0 < x < 1) and investigated their magnetic properties. Our study reveals that the variation of Ni and Mn content in Ni1-xMnxPS3 can efficiently tune the spin-flop transition, likely due to the modulation of the magnetic anisotropy. Such effective tunning offers a promising candidate to engineer 2D magnetism for future device applications.
The orthorhombic antiferromagnetic compound CuMnAs was recently predicted to be an antiferromagnetic Dirac semimetal if both the Ry gliding and S2z rotational symmetries are preserved in its magnetic ordered state. In our previous work on Cu0.95MnAs and Cu0.98Mn0.96As, we showed that in their low temperature commensurate antiferromagnetic state the b axis is the magnetic easy axis, which breaks the S2z symmetry. As a result, while the existence of Dirac fermions is no longer protected, the polarized surface state makes this material potentially interesting for antiferromagnetic spintronics. In this paper, we report a detailed study of the anisotropic magnetic properties and magnetoresistance of Cu0.95MnAs and Cu0.98Mn0.96As. Our study shows that in Cu0.95MnAs the b axis is the easy axis and the c axis is the hard axis. Furthermore, it reveals that Cu0.95MnAs features a spin-flop phase transition at high temperatures and low fields when the field is applied along the easy b axis, resulting in canted antiferromagnetism. However, no metamagnetic transition is observed in Cu0.98Mn0.96As, indicating that the magnetic interactions in this system are very sensitive to Cu vacancies and Cu/Mn site mixing.
Intrinsic antiferromagnetism in van der Waals (vdW) monolayer (ML) crystals enriches the understanding regarding two-dimensional (2D) magnetic orders and holds special virtues over ferromagnetism in spintronic applications. However, the studies on intrinsic antiferromagnetism are sparse, owing to the lack of net magnetisation. In this study, by combining spin-polarised scanning tunnelling microscopy and first-principles calculations, we investigate the magnetism of vdW ML CrTe2, which has been successfully grown through molecular beam epitaxy. Surprisingly, we observe a stable antiferromagnetic (AFM) order at the atomic scale in the ML crystal, whose bulk is a strong ferromagnet, and correlate its imaged zigzag spin texture with the atomic lattice structure. The AFM order exhibits an intriguing noncollinear spin-flop transition under magnetic fields, consistent with its calculated moderate magnetic anisotropy. The findings of this study demonstrate the intricacy of 2D vdW magnetic materials and pave the way for their in-depth studies.
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